Recently, accesses to Internet by means of a mobile terminal such as cellular phone and a hand-held information appliance through a mobile communication system increase.
In the case where a data communication is performed in order to access to home pages or to transmit and receive emails in a mobile communication system, a system wherein a transmission capacity that has been previously determined in accordance with circuit switching connection is allocated to each call has been heretofore employed.
Referring to FIG. 1, there is shown an example of a conventional mobile communication system for effecting a data communication in accordance with a circuit switching system comprising a mobile terminal 11, a radio base station 12, and a radio communication control unit 13 wherein a connection is established with respect to Internet 20 through a packet switching station (PDSN) 14, and a packet gateway switching station (PDGN) 15.
The mobile terminal 11 is a, user terminal in a mobile communication by the use of a cellular phone or a hand-held information terminal.
The radio base station 12 communicates with the mobile terminal 11 by means of transmission and reception of radio signals.
The radio communication control unit 13 is a control unit for controlling a plurality of radio base stations 12.
The packet switching station 14 is equipment to be connected with a call intending to link to Internet among calls to be connected with the radio communication control unit 13, which has a translating function between a communication switching system and a packet switching system.
The packet gateway switching system 15 is an interconnecting gateway switching station for connecting a data communication in a mobile communication system to Internet.
In case of a data communication through Internet link in a conventional mobile communication system, data is transmitted by means of a communication switching system inside the mobile communication system, then, the system is switched into a packet switching system in a packet switching system 14, and it is linked to Internet 20 in a packet gateway switching station 15.
Data communications such as Internet connections exhibit such characteristics that signals are transmitted and received for a short period of time in a burst mode different from voice communications, and no signal is transmitted and received other than the above-described period of time. In a communication switching system, a fixed band is allocated even during no signal is transmitted and received as same as in the case where signals are transmitted and received in a data communication, so that this means that a transmission capacity allocated is uselessly occupied in the case where no signal is transmitted and received. Accordingly, such situation as described above is a factor for preventing efficient use of a transmission capacity in data communication, and in this respect, improvements are demanded.
In place of such communication switching system, there is a packet system wherein a transmission capacity is efficiently used in data communication.
According to a packet system, a transmission capacity in a network is held in common with a plurality of terminals, so that packets are transmitted on the network in only the case where signals are transmitted and received by the terminals, and no transmission is effected other than the case described above. Therefore, such packet system is a system wherein a transmission capacity maintained by a network is efficiently utilized in accordance with statistical multiplexing effect in a data communication, which has such characteristic that signals are transmitted and received in a burst mode. Hence, utilization of the packet system increases also in a mobile communication system.
In also such packet system, packets transmitted from terminals and the like are restricted by means of an average value or a peak value in order to prevent convergence due to a concentration of the packets.
A mobile communication system involves a wireless line and a wired line wherein data is retransmitted frequently in order to transmit correctly the data, since wireless line exhibits a higher error rate than that of wired line. Furthermore, the lower quality in a wireless line brings about the slower practical data transmission speed. Besides, a larger amount of information for detecting errors and processing retransmission of signals is added to a wireless line than that of a wired line, so that a ratio of transmission capacity that can be utilized actually with respect to a line speed is lower in the wireless line than that of the wired line.
In this connection, since a substantially equal amount of transmission amount has been allocated to a wired line and a wireless line in a conventional mobile communication system, there was either a case where a transmission capacity in the wired line becomes useless in the event when quality in the wireless line becomes poor, or a case where abolishment of data arises in a part linked from the wired line to the wireless line.